WHAT IS MEANT BY PIPE SCHEDULING: SCH. 40 & SCH. 80

WHAT IS MEANT BY PIPE SCHEDULING: SCH. 40 & SCH. 80

First, pipe scheduling has nothing to do with the human concepts of time or schedules, rather, it is a defined measurement pattern. Scheduling is a fabrication plan used to specify a plumbing material's required total wall thickness depending on the full size of the pipe in terms of its width not its length. In other words, pipe scheduling is a set standard for how thick a pipe's wall must be based on how wide / large the pipe is in diameter.

You can think of pipe schedule as a data table that has been pre-filled with textbook standardized values for pipes and fittings. Manufacturers seeking to produce 2" Schedule 40 PVC pipe will know exactly how thick (at minimum) the pipe walls must be to be classified as a 2"; Schedule 40 PVC pipe. The exact wall thickness value requirements will differ on the specific pipe schedule intended and the plumbing's desired total width diameter.

By definition, as pipe schedule values increase, e.g. Sch. 40 versus Sch. 80, the pipe wall thickness also increases. This in turn indicates Schedule 80 pipe will always have thicker sidewalls when compared to Schedule 40 pipe, when used for a specified pipe size diameter and material. Between pipe schedules, the plumbing's wall thickness is the main variable / parameter that changes and corresponds to a change in the pipe's Inner Diameter (ID). The Nominal Pipe Size (NPS) and Outer Diameter (OD) measures for a given pipe are not affected by different pipe schedules -- e.g. a 6" NPS with a 6.625" OD will measure this way for either Sch. 40 or Sch. 80. The increased wall thickness between schedules occurs as a reduction in the Inner Diameter measurement.

HOW IS PIPE SCHEDULING USED

Pipe scheduling is used by contractors, construction and engineering firms as well as general plumbing handlers, installers and DIY (do it yourself) builders. Pipe schedules are used to understand the suitability of the pipe and/or fittings for their intended application(s). Whenever evaluating and comparing plumbing components and materials, professionals will choose the pipe size and schedule rating that has been designed and determined to meet and/or exceed the intended work demands. In simpler words, pipe scheduling is used to determine the plumbing equipment that is right for the job. In plumbing scenarios, it is important to compare and understand required pipe thickness, pressure ratings, chemical suitability and total costs, all of which are factors associated with and differ between pipe scheduling ratings.

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Comparing Schedule 40 and Schedule 80

Thickness -- Pipe wall thickness is the main physical difference between Sch 40 and Sch 80. The material thickness of pipes and fittings will be greater with higher number schedule ratings. Schedule 40 will have thinner walls than Schedule 80 for the specified pipe size. This means less material, which may mean a weaker product, which in turn can affect its project suitability if the integrity of the plumbing may be in question for the intended use. Thicker pipes, i.e. higher schedule pipes, will have greater structural and chemical durability, rigidity, and resilience to strain and pressure.

Pressure -- The maximum pounds per square inch (PSI) pressure rating for plumbing can be determined by its scheduling. Pipes and fittings with higher schedule numbers will be acceptable for greater pressure handling. Their service tolerance for increased fluid pressure is a direct result of the increased material thickness that is indicated by the pipe schedule. For pressurized liquid applications, Schedule 80 makes for a safer, more durable choice in general. However, Schedule 40 can be well suited if application pressure ranges are understood to be within the piping's determined parameters. See our table below that outlines the dimensions and working pressures for both Schedule 40 and Schedule 80 PVC piping.

NPS and Outer, Inner Diameter -- The Nominal Pipe Size (NPS) measurements for both Sch 40 and 80 piping will be the same for the same pipe size. NPS is similar to the pipe Outer Diameter (OD) measurement, which will also be the same for both schedule types. The Inner Diameter (ID) measurement is what differs between Sch 40 and Sch 80. In Sch 80, the additional material used increases the sidewall thickness on the inside of the plumbing only. This reduced inner diameter of Sch 80 accounts for a slight restriction in fluid flow through the pipe.

Cost -- Plumbing rated as Schedule 80 normally has a higher purchase cost over plumbing parts manufactured according to Schedule 40. The extra material that accounts for Sch 80's thicker sidewall, as well as the included colorant (if applicable) contribute to its increased cost.

Color -- Schedule 40 and 80 pipes often have a different color that is used to distinctly identify them. Sch 40 plumbing is traditionally natural white that lacks any color additives, while Sch 80 plumbing is traditionally a colored grey. Note that outliers to the norm often exist and specific manufacturers may not follow this common color pattern. While color can often indicate and contrast Sch 40 and 80 piping, always verify by reviewing the detailed info printed along the sides of pipes and fittings.

Installation -- Installation does not differ between Schedule 40 / 80 piping that has been made of the same material. According to ASTM standards, outside diameters will be equal across schedules of pipe that have equal NPS. This specification allows for pipes of different scheduling to be coupled together using the normal fittings and joining method for that piping material.

Corresponding Application & Use -- Due to the greater wall thickness of Schedule 80 plumbing, it is collectively understood to be stronger and more resistant than its Sch 40 counterpart. Plumbing applications that encounter increased pressure stress, mechanical strains, and/or chemical interactions often benefit from the use of a greater pipe schedule for the parts.

This is not to say Sch 80 is the best option simply because an application will transit liquids / water under pressure or handle chemicals. Rather, plumbing applications are extremely specific, especially those involving chemicals, and what is the best choice -- Schedule 40 or Schedule 80 -- will be an educated decision that considers the full variables of the pipe's intended use. If Sch 40 is acceptably rated for the operational conditions of the scenario, one can save both piping material and associated costs by choosing to use Schedule 40 over Schedule 80 plumbing.

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Property Table for Schedule 40 and Schedule 80 Plumbing: PVC & CPVC

The following property table overviews and compares Schedule 40 and Schedule 80 for its thickness, size, and maximum working pressure for fluids. Consider this chart and pressure ratings for pipe sizes whenever wanting to determine the compatibility of the pipe schedule for an application.

Schedule 40 & 80 PVC, CPVC Size & Operational Pressure Table

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